Fluorescent lamp and method of making



Jun 1958 J. SCHWING ETAL 2,338,707

FLUORESCENT LAMP AND METHOD OF MAKING Fil ed Sept. 15, 1956 in he 35INVENTORS JOSA-PH E JCHW/A/G Y 656410 SCH/AZZA/VO ,4 TTORA/EKS t es Patnt FLUORESCENT LAMP AND METHOD OF MAKING Joseph Schwing, Jersey City,and Gerald Schiazzano, Belleville, N. .J., assignors to Doro-TestCorporation, North Bergen, N. J., a corporation of New York ApplicationSeptember 13, 1956, Serial No. 609,654

4 Claims. (Cl. 313-109) This invention is composed of a discovery bymeans of which a certain type of fluorescent lamp which heretofore couldnot be made in the quick start form can now be so made.

There is in the fluorescent lighting art a. so called insect repellentlamp, which strictly is not a correct description of its function. Thefact is that an insect repellent lamp is a lamp having a color whichisless likely to attract insects because of its particular light spectrum.These lamps have a spectrum in which yellow and red predominate which isnot so readily seen by insects as are the usual fluorescent lamps havinga more normal or white light spectrum. Because of this characteristicthese so called insect repellent lamps are finding more and more use.Heretofore they have been made of the hot cathode type which arerelatively slower in starting and require the starter usually used forthe ordinary fluorescent lamp.

The purpose of this invention is to provide an improvement in insectrepellent lamps which adapt them to quick start operation.

Insect repellent lamps are caused to have a yellow, red spectrumpredominance by the use of a filter in the form of a coating of cadmiumsulphide which underlies the usual phosphor coating. The cadmiumsulphide coating filters the blues and greens of the transmitted lightof the glowing phosphor, resulting in a predominance of yellows and redsin its useful spectrum. Peculiarly enough, fluorescent lamps having acadmium sulphide light reflecting layer would not operate as quickstarting lamps.

In accordance with this invention it has been discovered that if finelydivided silicon dioxide is blended with the coating from which thecadmium sulphide layer is made, the lamp becomes capable of quick startoperation.

From the above the objects of this invention will be quite clear. a

In the accompanying drawings,

Figure 1 is a diagrammatic plan view of quick start insect repellentlamp of the type employing this invention;

and

' ported in these presses are the usual cathodes 16 and 18 which whenthe lamp is used as a quick start lamp will be of the usual electronemissive cold cathode construction. As shown in Figure 2, there may beassociated with each cathode a pair of horns 18' commonly used in suchlamps.

Likewise in accordance with prior practice, the tubular envelope isprovided at the ends with the usual caps 20 and 22 which in this caseare provided with the usual quick start contact structure 24 and 26, bymeans of which the lamp is mounted in the proper fixtures andelectrically connected in circuit.

Also in accordance with usual practice, the inner wall of the envelope10 is provided with a thin layer of cadmium sulphide which is overlaidwith the usual layer of phosphor or phosphor mixtures 30. Likewise thelamp during its manufacture is highly evacuated and is provided with anatmosphere of argon and mercury vapor supplied by a small quantity ofmercury introduced into the envelope during its manufacture. Such a lampas described will not operate as a quick start lamp. However, byincorporating in the cadmium sulphide coating finely divided silicondioxide, the lamp becomes an instant start lamp.

Experiments demonstrate that the amount of silicon dioxide employed isnot critical. It has been found that insect repellent lamps will quicklystart in many cases if,

as little as one percent by weight of silicon dioxide is incorporated inthe cadmium sulphide coating. At the other end of the range it can besaid that theoretically as much as by weight can be included, but fromthe viewpoint of insect repellent lamps it has been found that thehigher the percentage of silicon dioxide in the cadmium sulphidecoating, the more and more is that coatings filtering functiondestroyed. Experiments indicate that for commercial purposes about 50%by weight of silicon dioxide can be incorporated in the cadmium sulphidelayer. This much silicon dioxide does change the light filtercharacteristics of the cadmium sulphide spectrum to some degree, butthis change can be counterbalanced by changing the phosphor or mixturesthereof of which the fluorescent coating 30 is composed.

The following procedure is employed to produce the above described lamp.A coating consisting of the following ingredients is prepared as asuspension:

Cadmium sulphide grams 132 Nitro-cellulose cc 320 Butyl acetate cc 1281Dibutyl phthalate cc 50 This mixture is ground in a ball mill for aboutsixteen hours, producing a suspension suitable for the purpose. Thenitro-cellulose and butyl acetate act as organic carriers for thecadmium sulphide which can later be evaporated and baked out of thecoating. The dibutyl phthalate is used as a plasticizer and is but oneexample of a large number of plasticizers which would be suitable for acoating of this kind, as those skilled in the art will understand.

The silicon dioxide is also incorporated into a suspension composed ofthe following ingredients:

Silicon dioxide grams 260 Nitro-cellulose cc 480 Butyl acetate cc 3385Dibutyl phthalate cc 50 This mixture is also further ground in a ballmill for approximately sixteen hours.

A suitable form of silicon dioxide for the purposes of this invention iscommercially available under the name Hi-Sil, manufactured and sold byColumbia Southern Chemical Company. It is suitable because it'has beenfound that the more finely divided the silicon dioxide the more efiective it is for the purposes of this invention. Hi-Sil happens to providea finely divided form of a silicon dioxide which is still more finelydivided by the ball mill referred to. Here again, as before, thecarriers and plasticizers function as mentioned above and are providedfor similar purposes.

The two suspensions prepared as above are then mixed in equal quantitiesby volume, providing afinal suspension-which is' 'coated on the envelope10 to provide the layer 28 of Figure 2. This coating is then baked toevaporate and remove the liquid carriers.

The coated envelope is then coated with the phosphor or'mixtures thereofselected for use,'and of course, again baked to removeits volatilecarriers.

' 'After the envelopeis highly-evacuated in accordance with usualpractice, it is filled in'the usual manner, for example with about 2 /2millimeters or argon gas and 50 milligrams-of mercury. Of course, allthe other process ing steps commonly usedin making such lamps will beemployed.

There is another advantage of the coating 28'which has beenobserved,-namely that-there is a tendency for the lamps to have lessdarkened "ends as its useful life develops The phenomenon of darkenedends in fluorescent lamps is well'known, and it is only'noted here thatthe presence of silicon dioxide seemsto'tend' to reduce the tendency ofdarkened en'ds'to 'occur as the lamp grows older in use.

From the above description it will be apparent to those skilled in theart that the substance of this invention is capable of some variation indetail, and it is preferred, therefore, that the material hereincontained be taken in an exemplary sense.

4 What is claimed is: 1. A quick starting fluorescent lamp having atransparent envelope coated on its inner face with a coating containingcadmium sulphide and silicon dioxide overlaid with a phosphor coating.

2. In the combination of claim 1, said silicon dioxide being present inthe proportions of two to seventy-five percent by weight.

3. In the combination of claim 1, said cadmium sulphide'and silicondioxide being present in substantially equal proportions.

4. In the method of manufacturing a quick starting fluorescent lamp thestepsof milling a mixture of cadmium sulphide, a volatile organiccarrier and a plasticizer, milling a mixture of finely divided silicondioxide, a volatile organic carrier and a plasticizer, mixing saidmilled mixtures, coating a fluorescent tube envelope with said finalmixture and baking said coating.

References Cited in the file of this patent UNITED STATES PATENTS2,329,632 Marsden Sept. 14, 1943 2,441,559 Paramus et a1. May 18, 19492,607,014 Roy et ah Aug. 12, 1952 2,687,486 Heine et al. Aug. 24, 19542,706,262 Barnes Apr. 12, 1955

